1. Field of the Invention
The present invention relates to high fidelity acoustic data processing or compression.
2. Description of the Related Art
Directional acoustic data is useful for a wide range of applications from surveying underground structures to tracking bodies traveling underwater. This data usually comprises acoustic pressure measurements sampled to resolve acoustic frequencies between a few cycles per second (Hertz, Hz) to a few kiloHz (kHz, 1 kHz=103 Hz) along each of multiple directions of arrival, called beams. Multiple beams are detectable by one dimensional (1D), two dimensional (2D) and three dimensional (3D) arrays of acoustic sensors, called acoustic arrays herein. Sampling rates approach counts of pressure samples per second at twice the highest frequency for each beam. Since a pressure measurement usually involves about 8 binary digits (bits) of data for each of tens to hundreds of beams, data rates can exceed 100 megabits per second (Mbps, 1 Mbps=106 bits per second).
When the directional acoustic data is collected at remote sites, the data must be communicated to a processing station over a communications channel, such as a satellite communications channel, that might have a very limited bandwidth compared to the bandwidth of several hundred MegaHertz (MHz, 1 MHz=106 Hz) needed to carry such high data rates, Therefore, it is desirable to represent the important features of the directional acoustic data in less than the full data rate, a process called compression. An acoustic compression technique well known in the art that preserves the human-perceptible nuances of speech and music is the Moving Picture Experts Group (MPEG) Audio Layer III (MP3) format for audio data. MP3 can achieve a compression ratio (ratio of uncompressed data rate to compressed data rate) of about 7:1 or 8:1. For some applications, however, including some applications for directional acoustic data, the MP3 compression ratio is insufficient; and compression ratios of 16:1 to 24:1 and greater are desirable. However, the compressed data should preserve important features for acoustically detecting or characterizing objects such as subsurface structures and underwater bodies.